Natalia V. Bulina

Ti3SiC2-Cu composites by mechanical milling and spark plasma sintering: Possible microstructure formation scenarios

We present several possible microstructure development scenarios in Ti3SiC2-Cu composites during mechanical milling and Spark Plasma Sintering (SPS). We have studied the effect of in situ consolidation during milling of Ti3SiC2 and Cu powders and melting of the Cu matrix during the SPS on the hardness and electrical conductivity of the sintered materials. Under low-energy milling, (3–5) vol.%Ti3SiC2-Cu composite particles of platelet morphology formed, which could be easily SPS-ed to 92–95% relative density. Under high-energy milling, millimeter-scale (3–5) vol.%Ti3SiC2-Cu granules formed as a result of in situ consolidation and presented a challenge to be sintered into a bulk fully dense sample; the corresponding SPS-ed compacts demonstrated a finer-grained Cu matrix and more significant levels of hardening compared to composites of the same composition processed by low-energy milling. The 3 vol.% Ti3SiC2-Cu in situ consolidated and Spark Plasma Sintered granules showed an extremely high hardness of 227 HV. High electrical conductivity of the Ti3SiC2-Cu composites sintered from the granules was an indication of efficient sintering of the granules to each other. Partial melting of the Cu matrix, if induced during the SPS, compromised the phase stability and uniformity of the microstructure of the Ti3SiC2-Cu composites and thus it is not to be suggested as a pathway to enhanced densification in this system.

Magnetic Anisotropy in the Films of Oriented Carbon Nanotubes Filled with Iron Nanoparticles

Films of carbon nanotubes oriented perpendicularly to the substrate surface and filled with iron nanoparticles have been synthesized and studied. Morphological features of these nanocomposite films lead to the appearance of an easy magnetization axis, which is perpendicular to the film plane. A method for enhancement of this effect is suggested and successfully tested.

Crystal structures of chloroform solvates of fullerenes

The chloroform solvates of C60 and C70 fullerenes and of the C60/C70 mixture were synthesized and investigated by X-ray powder diffraction.

Detonation Spraying of Ti–Al Intermetallics: Phase and Microstructure Development of the Coatings

The goal of this work was to study the phase and microstructure changes involved in the process of coating formation by detonation spraying of Ti3Al, TiAl, and TiAl3 intermetallics. The O2/C2H2 ratio was varied between 1.1 and 2.0, and the explosive charge was 30–40% of the barrel volume. In most experiments air was used as a carrier gas; selected experiments were performed with argon. We found that depending on the spraying parameters, TiAl3 essentially retains in the coatings or partially decomposes forming TiAl and Ti3Al as minor phases. Detonation sprayed Ti3Al reacts with nitrogen and oxygen partially transforming into titanium nitrides TiN/Ti2N and titanium oxynitrides TiNxOy. TiAl partially decomposes forming Ti3Al, which further reacts with oxygen and nitrogen as the particle temperature and the content of oxygen in the explosive mixture increase. The in situ formed titanium nitrides and oxynitrides show a reinforcing effect increasing the hardness of the coatings.

Specific features of polyol synthesis of silver nanoparticles with the use of solid carboxylates as precursors

Electron microscopy, X-ray diffraction, and chromatography-mass spectrometry have been employed to investigate the reduction of solid silver caprylate in ethylene glycol with the formation of silver nanoparticles. The structural characteristics of silver nanoparticles have been studied as depending on the conditions of their synthesis, including temperature, reduction time, and silver salt concentration. It has been found that, in the studied range of parameters under the conditions, when solid silver caprylate is dispersed in ethylene glycol, the characteristics of resulting nanoparticles are almost independent of the synthesis temperature. This peculiarity is related to the fact that the formation and growth of nanoparticles occur on the surface of silver salt crystals and are accompanied by gradual dissolution thereof. In this system, ethylene glycol plays the roles of a reductant and a solvent for liquid reaction products.

Structural and particle size characteristics of lithium carbonate after mechanical activation and heat treatment

This paper examines the structural and particle size characteristics of lithium carbonate after mechanical processing in an AGO-2 planetary activator, followed by heat treatment. Milling increases the specific surface area of lithium carbonate, changes the aggregate size distribution, reduces the crystallite size, increases the lattice strain in the material, and changes the monoclinic cell parameters. Subsequent heat treatment of the mechanically activated samples in the range 25–500°C is accompanied by recrystallization of the material: its specific surface area and lattice strain decrease, the crystallite size increases, and its unit-cell parameters change.

Laser-induced reactions in layers of B4C + Fe and B + C + Fe mixtures on a steel substrate

We have studied laser-induced processes in layers of mixtures of boron carbide and iron or a stoichiometric mixture of boron with carbon (4: 1) and iron on a steel substrate. Laser processing was found to increase the microhardness of the surface owing to the formation of a coating containing iron boride phases: Fe2B and Fe3B. After preliminary mechanical activation of boron carbide and iron mixtures, even the lowest laser power used in the experiments was enough to initiate the formation of iron borides.

Crystallization of Ti33Cu67 metallic glass under high-current density electrical pulses

AbstractWe have studied the phase and structure evolution of the Ti33Cu67 amorphous alloy subjected to electrical pulses of high current density. By varying the pulse parameters, different stages of crystallization could be observed in the samples. Partial polymorphic nanocrystallization resulting in the formation of 5- to 8-nm crystallites of the TiCu2 intermetallic in the residual amorphous matrix occurred when the maximum current density reached 9.7·108 A m-2 and the pulse duration was 140 μs, though the calculated temperature increase due to Joule heating was not enough to reach the crystallization temperature of the alloy. Samples subjected to higher current densities and higher values of the evolved Joule heat per unit mass fully crystallized and contained the Ti2Cu3 and TiCu3 phases. A common feature of the crystallized ribbons was their non-uniform microstructure with regions that experienced local melting and rapid solidification. PACS: 81; 81.05.Bx; 81.05.Kf.

Thin fullerene-containing films synthesized by ion beam sputtering of fullerene mixtures with doping additives in vacuum

A new approach to the synthesis of films containing fullerenes and doping elements is described. It is suggested that a cluster mechanism of the target sputtering by accelerated ions makes possible the deposition of fullerenes on a substrate with a certain probability for dopant atoms being introduced into the cavities of fullerene molecules and a higher probability of their occurrence between fullerene molecules. The proposed method has been experimentally implemented by using an Ar+ ion beam to sputter C60/C70 fullerene mixtures (synthesized in a plasmachemical reactor at a pressure of 105 Pa) pressed into disk targets with a doping element (Fe, Na, B, Gd, or Se). The ion beam sputtering of dopant-containing fullerene mixtures in a vacuum of ∼10−2 Pa allowed micron-thick films containing C60 and C70 fullerenes and the corresponding dopant element (Fe, Na, B, Gd, or Se) to be grown on quartz substrates.

Synthesis of nonspherical nanoparticles by reducing silver neodecanoate extract with benzyl alcohol

A method for synthesizing nonspherical silver nanoparticles by reducing liquid extract of silver neodecanoate in benzyl alcohol has been developed. The method is simple and does not require the use of polyvinylpyrrolidone, sodium citrate or special methods using pre-synthesized seeds. The obtained particles have been investigated by the methods of electron microscopy, X-ray diffraction, and differential-thermogravimetric analysis. It has been found that triangular and hexagonal plates, as well as particles of pentagonal form and polyhedrons, are formed as a result of the reduction. The sizes of the obtained plates, depending on the synthesis conditions, vary from 80 nm to 2 μm. The method is promising for the industrial production of silver nano- and microplates.